On the architecture of elytra 191

Entomologie heute 22 (2010): 191-204

On the Architecture of Beetle Elytra

Zur Architektur von Käferelytren

THOMAS VAN DE KAMP & HARTMUT GREVEN

Summary: We examined the elytron cuticle of various beetle species histologically and by scanning electron microscopy (SEM). All cuticles examined appear to be of pseudorthogonal type, i.e., single orthogonal layers of microfibrils are delineated by intervening helicoidal microfibrils. In the endocuticle two “types” of “lamellae” (i.e. cuticular layers visible in histological sections) can be distinguished. One type is characterised by successive plies of unidirectional arranged microfibrils, in the other the plies are subdivided in paralleling rods consisting of thick bundles (macrofibres) of microfibrils that are unidirectional oriented along the bundle. Transitional stages between the two types are expected to occur. Successive plies and successive bundles cross at various angles. The “type” with the macrofibres corresponds to the “balken cuticle” of the classical German literature. Further, data from the elytra of 40 beetle species of 24 families point to the considerable variation regarding the total thickness of an elytron, the thickness of the dorsal and ventral cuticle of an elytron and the width of the hemolymph space within elytra.

Key words: cuticle, elytra, “balken”, pseudorthogonal cuticle

Zusammenfassung: Wir haben die Elytrencuticula verschiedener Käferarten histologisch und mit Hilfe des Rasterelektronenmikroskops (REM) analysiert. Wir gehen davon aus, dass alle untersuchten Cuticulae vom pseudorthogonalen Typ sind, d. h., dass die einzelnen orthogonalen Lagen aus Mikrofibrillen von helicoidal angeordneten Mikrofibrillen begrenzt werden. In der Endocuticula sind zwei „Typen“ von „Lamellen“ (einzelne Lagen der Cuticula im histologischen Schnitt) zu unterscheiden, die wahrscheinlich durch Übergänge miteinander verbunden sind. Ein „Typ“ ist durch Lagen mehr oder weniger flächiger Schichten einheitlich ausgerichteter Mikrofibrillen charakterisiert, im zweiten „Typ“ bestehen diese Lagen aus parallel liegenden, weitgehend getrennten, dicken Bündeln (Makrofibrillen) von Mikrofibrillen, die einheitlich längs des Bündels ausgerichtet sind. Aufeinander gestapelte Lagen und Bündel kreuzen sich unter verschiedenen Winkeln. Der „Typ“ mit den parallelen Makrofibrillen entspricht der „Balkencuticula“ der klassischen deutschsprachigen Literatur. Zudem belegen wir bei 40 Käferarten aus 24 Familien eine beträchtliche Variation in der Dicke der gesamten Elytre, auffallende Unterschiede in der Dicke der Cuticula der ventralen und dorsalen Cuticula sowie der Ausdehnung des Hämolymphraums zwischen beiden.

Schlüsselwörter: Insektencuticula, Elytren, Balken, pseudorthogonale Cuticula

1. Introduction multilayered, being divided into an outermost epicuticle preceded by the chitin containing The insect cuticle is a multifunctional procuticle, in which a dense exo- (= preecdysal lightweight composite material, which has procuticle) and a thicker endocuticle may be over the years attracted much attention in distinguished. This holds also for the elytra, various fields (summarized e.g. by RICHARDS fore wings in the Coleoptera that cover the 1951; NEVILLE 1975, 1993, 1998; VINCENT & membranous hind wings, when the latter are WEGST 2004). As seen throughout the folded up at rest. Elytra develop from the , the adult insect cuticle is imaginal discs and are principally evaginations

Entomologie heute 22 (2010) 192 THOMAS VAN DE KAMP & HARTMUT GREVEN of the epidermis. Therefore they exhibit an When checking the literature, we became aware outer (dorsal) and an inner (ventral) cuticle, of two “types” of pseudorthogonal cuticles. which enclose the haemolymph space One “type” has successive layers (“plies”) traversed by trabeculae, which connect upper made up of microfibrils with a unidirectional and lower elytral surfaces. Elytra of orientation (for the first time described in are “hard” and highly sklerotised (see Tenebrio molitor: NEVILLE & LUKE 1969; textbooks of entomology). NEVILLE 1975). The other “type” shows Exo- and endocuticle often show unit layers parallel bundles (macrofibres) of tightly termed “lamellae” when viewed under the packed microfibrils orientated unidirectional light microscope, but more so when studied along the bundle, which are separated from with the transmission electron microscope. each other by a small gap, or macrofibres may In sections through the cuticle of , form a network (see below). Macrofibres parabolic arcs (BOULIGAND 1965) or spiral change their direction in successive layers (e.g. patterns of microfibrils (e.g. MEYER-ROCHOW marginata, HEPBURN 1972; HEPBURN 1975) are frequently visible under both LM & BALL 1973; DENNELL 1976; GREVEN & and TEM, but as explained in detail by SCHWINGER 2005). The bundles of BOULIGAND (1972) and others, these patterns macrofibres correspond to the “balken” are optical artifacts. The cuticle consists of described in the classical German literature laminae of chitin microfibrils that run parallel (summarized in RICHARDS 1951). MEYER to the cuticle surface and are embedded in a (1842; fide BIEDERMANN 1903) was the first, protein matrix. Within each lamina the who found that each “lamella” in the cuticle microfibrils are oriented in the same direction, of Lucanus cervus was composed of parallel but in successive laminae there is a slight and partly anastomosing “clear rods” (“glas- rotation in orientation, and for every 180o a helle Stäbchen”) and that successive lamellae lamella is observed in sections normal to the crossed at various angles. In Oryctes nasicornis surface. these rods, however, form a network (see also In cuticles of other species, however, KAPZOV 1911). The term “balken” or “balken- unidirectional oriented microfibrils form a lage” was introduced by KAPZOV (1911), who preferred layer (“ply”), which represents noticed that “balken” might fuse to form a strictly speaking a thick lamina. Most of more or less continuous “lamella” (see also them do not consist exclusively of uni- KÜHNELT 1928). directional “plies”, i.e. they are not strictly In later articles, authors did not clearly orthogonal, but “plies” exhibit a thin differentiate between continuous plies and intervening layer of helicoids. Therefore, “balken”. STEGEMANN (1930: p. 11) wrote that these systems have been called pseud- the “balkenlage” of the elytra in Cicindelae orthogonal (see the two-system model for (sic!) consisted of clear plates with parallel chitin-protein complexes in insect cuticles fibrils and similarly SPRUNG (1932: p. 447) by NEVILLE & LUKE 1969; see also NEVILLE described for the elytra of Carabidae “Balken- 1975, 1993, 1998): lagen”(p. 447) consisting of fibrous chitin

Fig. 1: Some beetles, whose elytra were studied (shown to scale). Abb. 1: Einige Käferarten, deren Elytren untersucht wurden (im richtigen Größenverhältnis zu- einander). A Pterostichus niger (Carabidae). B aurata (Cetoniidae). C stercorosus (Scarabaeid- ae). D Tenebrio molitor (Tenebrionidae). E fastuosa (Chrysomelidae). F Ceutorhynchus palli- dactylus (). G Trigonopterus nasutus (Curculionidae). H Sitophilus granarius (Curculioni- dae). I Phyllobius betulinus (Curculionidae). On the architecture of beetle elytra 193

Entomologie heute 22 (2010) 194 THOMAS VAN DE KAMP & HARTMUT GREVEN

Tab. 1: Thicknesses of the elytra and widths of cuticular layers, occurrence of plies and “balken”, size of the hemolymph space and capability of flight (indicated by symbols) of the beetle species examined. All measurements in µm. *Exocuticle of the ventral cuticle; **the small values refer to the elytral grooves, ***measurements above the haemolymph space. el = overall thickness of On the architecture of beetle elytra 195 layers (“fibrilläre Chitinschichten”; p. 447). were from the collection of the State Museum Later, DENNELL (1976; p. 162) distinguished of Natural History in Karlsruhe (SMNK). Most clearly between ”layers of bundles” (= balken; of them were stored in ethanol. see also DENNELL 1978) and “layers of For light microscopy small pieces of the elytra horizontally disposed fibres”. In the more were dehydrated and embedded in epoxy resin recent literature, especially studies focusing on (SPURR 1969). Semithin sections, approx. 0.5 the mechanical properties, only µm thick, were made with a Reichert OM U3 pseudorthogonal cuticles without further microtome using glass knifes and stained differentiation are mentioned and occasionally with toluidin- blue-borax. Photos were edited the cuticle structure is insufficiently described with Adobe Photoshop CS3. Measurements (e.g. CHEN & FAN 2004; YANG et al. 2010 and (see Table 1) were taken from sections of a references therein). single specimen of each species. Apart from the histological studies mentioned For scanning electron microscopy (SEM) above and a histological study comparing the dried elytra were broken vertically with two thickness of the various lamellae and the fine forceps. The pieces were glued to stubs, proportions of exo - and endocuticle in the sputtered with gold and examined under a elytra of 36 beetle species (KRZELJ 1969), Zeiss LEO 1430VP scanning electron detailed comparative studies of beetle elytra microscope. In some preparations the angle using transmission and scanning electron between two successive plies or “balken” microscopy, are largely missing. could be estimated by viewing the samples From a wider study concerning the possible directly from above. phylogenetic significance of the architecture Abbreviations used in the figures 2 and 3: en of the elytron cuticle (in preparation) we = endocuticle, ep epicuticle, ex = exocuticle, selected the elytra of 14 beetle species to hs = hemolymph space, tr = trabecula. illustrate the classical “balken cuticle” and other pseudorthogonal cuticles employing 3. Results histological sections and scanning electron microscopy (SEM). Further, we give some Dorsal (upper) and ventral (lower) parts of measurements of the elytra from altogether an elytron are separated by a haemolymph 40 beetle species of 24 families and to call space created by cuticular columns, the attention to some topics insufficiently studied trabeculae. Figure 3 shows sections of the or not at all studied. elytra of some of the beetles examined. Table 1 gives some measurements of the dimen- 2. Material and methods sions of the elytron cuticles and some of their constituents in 40 beetle species. Elytra of the 40 beetle species examined herein The thickness of the total elytron varies (some of them are shown in Fig. 1; see Table 1) considerably across species, but also in elytron; uns = thickness of under side; ups = thickness of upper side; ex = exocuticle thickness; lay = unidirectional endocuticle layers counted (upper side); ty = endocuticle type; hs = size of hemolymph space. Tab. 1: Dicke der gesamten Elytre und einzelner Cuticulaschichten, Vorhandensein von Lagen und Balken, Größe des Hämolymphraumes und Flugfähigkeit (durch Symbole gekennzeichnet) der untersuchten Käferarten. Alle Angaben in µm. *Exocuticula der Unterseite, **die kleinen Werte beziehen sich auf die Rillen in den Elytren; ***Messung über dem Hämolymphraum. el = Gesamt- dicke der Elytren; uns = Dicke der Unterseite; ups = Dicke der Oberseite; ex = Dicke der Exocuticula; lay = Unidirektionale Lagen in der Endocuticula (Oberseite); ty = Typ der Endocu- ticula; hs = Größe des Hämolymphraums.

Entomologie heute 22 (2010) 196 THOMAS VAN DE KAMP & HARTMUT GREVEN On the architecture of beetle elytra 197 different regions of an elytron. Further, the In S. granarius (Fig. 2 A), C. pallidactylus (Fig. ventral cuticle is always thinner than the dorsal 2 B), P. niger (Fig. 2 D) and A. stercorosus (Fig. one. Also the extension of the haemolymph 2 E), semithin sections allow distinguishing space is extremely variable (Fig. 2). This space the thin brown-stained epicuticle from the is very small in the compact elytron of the largely lamellate procuticle in both, the ventral Sitophilus granarius (Fig. 2 A), somewhat and dorsal part of an elytron. The procuticle wider in the elytron of other such as could be clearly divided in exo- and Ceutorhynchus pallidactylus (Fig. 2 B) and endocuticle by means of the narrower Phyllobius betulinus (Fig. 2 C), medium-sized “lamellae” in the former. In some cases – A. in the carabid Pterostichus niger (Fig. 2 D), and stercorosus (Fig. 2 E) and C. aurata (Fig. 2 F) –, considerably larger in the scarabaeid the exocuticle does not show typical (Fig. 2 E) and the “lamellae”. The course of “lamellae” is more cetoniid Cetonia aurata (Fig. 2 F). or less horizontal; in the trabeculae “lamellae”

Fig. 3: Pseudorthogonal cuticles of elytra with “plies” (A, B) and “balken” (C, D). Semithin sections. Abb. 3: Pseudorthogonale Cuticulae der Elytren mit Platten (A, B) und Balken (C, D). Semidünn- schnitte. A Tenebrio molitor. B Anoplotrupes stercorosus. C Cetonia aurata. D Trigonopterus nasutus.

Fig. 2: Variously sized hemolymph spaces of the elytra. Semithin sections. Abb. 2: Unterschiedlich große Hämolymphräume der Elytren. Semidünnschnitte. A Sitophilus granarius. B Ceutorhynchus pallidactylus (Curculionidae). C Phyllobius betulinus. D Pterosti- chus niger. E Anoplotrupes stercorosus. F Cetonia aurata.

Entomologie heute 22 (2010) 198 THOMAS VAN DE KAMP & HARTMUT GREVEN On the architecture of beetle elytra 199 are arranged vertically (Fig. 2 F). “Lamellae” or rods of different sizes. These rods clearly are variously thick in a given elytron (Tab. 1). change their direction in successive layers either At least in the endocuticle two “types” of abruptly at an angle of 90o, which leads to cuticle can be distinguished already by LM (Fig. alternating cross- and longitudinal sectioned 3). In “type” 1 the lamellae consist of more “balken” in successive layers such as in C. or less continuos “plies” as in P. niger (Fig. 2 aurata (Fig. 3 C), or at smaller angles, which D), T. molitor (Fig. 3 A) and A. stercorosus (Fig. results in variously obliquely sectioned 3 B). In “type” 2 the “plies” seem to be broken “balken” limited by longitudinal sectioned down in single parallel strands (= “balken”) “balken” after a rotation of the layers of 180o

Fig. 5: Angles between the successive “plies” (A) and “balken” (B-D) in the elytron cuticle. Angles do not correspond exactly to the angles really determined (see “Material and methods”). SEM images. Abb. 5: Winkel zwischen den übereinanderliegenden Platten (A) und Balken (B-D) in der Elytren- cuticula. Die Winkel entsprechen nicht den tatsächlich gemessenen (s. „Material und Methoden“). REM-Aufnahmen. A Anoplotrupes stercorosus. B Timarcha metallica (Chrysomelidae). C Trigonopterus nasutus. D Gymnopho- lus subnacreus (Curculionidae).

Fig. 4: Pseudorthogonal cuticles of elytra with “plies” (A-D) and “balken” (E-H). SEM images.. Abb. 4: Pseudorthogonale Cuticulae der Elytren mit Platten (A-D) und Balken (E-H). REM- Aufnahmen. A Tenebrio molitor. B ochraceus (Byturidae). C Pterostichus niger. D Anoplotrupes stercorosus. E Cetonia aurata. F Anthaxia fulgurans (Buprestidae). G Chrysolina fastuosa. H Otiorhynchus ovatus (Cur- culionidae).

Entomologie heute 22 (2010) 200 THOMAS VAN DE KAMP & HARTMUT GREVEN as in the weevil Trigonopterus nasutus (Fig. 3 stercorosus the layer shows a fine vertical D; see also Fig. 2 A, B). striation (Fig. 4 D), which is seen also in the Fractures of the elytra examined by SEM histological section (Fig. 3 B). The bulk of confirm and broaden the histological analysis. procuticles is organized either in “plies” (Fig. The outermost layer appears as a dense solid 4 A-D, 5 A) or in more or less compact strands material, which bears the surface micro- or balken (Fig. 4 E-H, 5 B-D). In some cases sculpture of the elytron (e.g. Fig. 4 C). also “plies” and “balken” occur in a given Although this layer is likely to be the epicuticle, endocuticle such as in the buprestid Anthaxia it cannot clearly be differentiated from the fulgurans (Fig. 4 F) and in the weevil underlying exocuticle (Fig. 4 B, G). Only in A. Otiorhynchus ovatus (Fig. 4 H).

Fig. 6: Diagram of the variation of pseudorthogonal endocuticles of beetle elytra. “Plies” and “balken” cross at 90°. A Pseudorthogonal cuticle with continuous “plies”. B Pseudorthogonal cuticles with single “balken”. The organisation of the exocuticle (ex) is not pseudorthogonal and variable. Presence of helicoids between “plies” and “balken” was not documented in the herein examind elytra. For further explanations see text. Abb. 6: Schema von zwei unterschiedlichen Ausprägungen der pseudorthogonalen Endocuticula von Käferelytren. Die Lagen und die Balken sind jeweils um 90° versetzt. A Pseudorthogonal mit mehr oder weniger flächigen Lagen. B Pseudorthogonale Cuticla mit einzelnen Balken. Die Orga- nisation der Exocuticula (ex) ist nicht pseudorthogonal und variabel. Die helicoidalen Laminae zwischen den Platten und Balken sind bei den hier untersuchten Elytren noch nicht nachgewiesen. Weitere Erklärungen s. Text. On the architecture of beetle elytra 201

Angles at which the plies or “balken” cross studies would be promising, which, however, are difficult to determine in the fractures. In a should consider a variety of other parameters few cases a reliable estimation was possible. like for instance, the spacing and dimensions In C. aurata (Fig. 4 E) and Timarcha metallica of the trabeculae crossing the haemolymph (Fig. 5 B) „balken“ cross at angles of approx. space, size and weight of the beetle, size of 90o. The same holds for the plies of A. the flight muscles etc. stercorosus (Fig. 5 A), whereas “balken” in Elytra of Coleoptera are denoted as heavily Trigonopterus nasutus (Fig. 5 C) cross at angles sclerotized. Generally it is the exocuticle that of 30 to 60o and in Gymnopholus ovatus (Fig. 5 has a dense chitin-protein structure and D) of 60 to 90o (for further data see Table 1). becomes hard and stiff due to sclerotization (e.g. NEVILLE 1975, 1993). KRZELJ (1969) 4. Discussion observed in the elytra of 36 beetle species a layer dyed red after Mallory-Heidenhain, which Elytra of beetles are lightweight, mul- he denominated exocuticle and which tifunctional structures. They behave accounted for 65-85% of the cuticle thickness. mechanically as a composite material (as insect The “typical” fully sclerotized cuticle after cuticle in general) with a good resistance to Mallory staining is amber, brown or black in bending and compression, serve among the outer portions (exocucticle), red in the others to protect the hind wings and the body central layers (mesocutcicle = exocuticle in the and produce significant aerodynamic forces “soft” state) and blue in the inner portions in those beetles, which fly with their elytra (endocuticle) (for staining and terminology extended laterally (e.g., NACHTIGALL 1964; see RICHARDS 1951; NEVILLE 1975). However, SCHNEIDER & HERMES 1976; NEVILLE 1993; in the few studies on beetle elytra using TEM DE SOUZA & ALEXANDER 1997). and SEM, authors denominate the bulk of Certainly, saving of material contributes to elytron cuticles as endo- or mesocuticle (e.g. the light-weight construction of elytra. This HEPBURN 1972; LEOPOLD et al. 1992). may be achieved by reducing their overall Exocuticles may be exclusively helicoidal thickness, the thickness of the ventral cuticle throughout their thickness and “lamellae” are and/or the enlargement of the hemolymph generally narrower than in the endocuticle, but space. Figures 2 and 3 show sections through other configurations may also occur, i.e. the elytra of three species, which are flightless division in a superficial part where fibres are and exhibit relatively small haemolymph oriented nearly perpendicular to the surface spaces (Pterostichus niger, Trigonopterus nasutus, and a deeper part with fibres parallel to the Sitophilus granarius) and five species, which are surface (NEVILLE 1967, 1998; BARBAKADZE et able to fly having relatively large haemolymph al. 2006). The LM and SEM-techniques spaces (Cetonia aurata, Anoplotrupes stercorosus, applied herein did not allow a clear classi- Tenebrio molitor, Ceutorhynchus pallidactylus, fication of this layer. Phyllobius betulinus). These very rough The bulk of the cuticle of the beetle elytra estimations and the additional measurements examined appears to be organized in the given in table 1 are highly suggestive. Sur- pseudorthogonal fashion which has been prisingly, we did not find reliable data in the described for the cuticle of other Coleoptera literature to substantiate our assumptions. (e.g., HEPBURN 1972; ZELAZNY & NEVILLE KRZELJ (1969) gave numerous measurements 1972; NEVILLE 1975, 1993). The thin of the thicknesses of the various layers of postulated intervening layers of helicoidal the elytron cuticle of beetles, but focused the lamellae between the layers could not be discussion on the proportion of exo-and adequately resolved by the techniques used endocuticle in the elytra. We think comparative herein (light microscopy, scanning electron

Entomologie heute 22 (2010) 202 THOMAS VAN DE KAMP & HARTMUT GREVEN microscopy). However, to our knowledge “fibrous matrix” that was extractable with these helicoids have not been adequately KOH (LEOPOLD et al 1992). documented in any beetle elytron. HEPBURN Angles, at which plies or “balken” cross, may (1972) and HEPBURN & BALL (1973) have vary. Very common are angles of 90o, but shown by LM, TEM and SEM that in smaller ones have also been reported Pachnoda sinuata the parallel macrofibres of (BIEDERMANN 1903; KÜHNELT 1928; one horizontal layer are connected by “intra- STEGEMANN 1929; ZELAZNY & NEVILLE 1972; ply” cross linking fibres and those of HEPBURN 1972, HEPBURN & BALL 1973; successive layers by “interply” fibres. On the DENNELL 1976; 1978; GREVEN & SCHWINGER TEM pictures of the “balken cuticle” of the 2005); angles may even depend on the weevil Anthonomus grandis shown by LEOPOLD cuticular region. For example, “balken” in the et al. (1992) no helicoids between the often elytral cuticle of Cybister sp. cross at 90o tightly adjacent successive “balkenlagen” can throughout the bulk of the cuticle, at be recognized. approximately 60o in the innermost region, Our survey confirms the existence of two but do not cross in deeper layers of the femur “types” of pseudorthogonal cuticles cuticle (DENNELL 1978). A computer-aided (summarized in Figure 6). One “type” has determination showed that each successive “lamellae” (as identified in histological layer of macrofibres in the sclerites of the sections) formed by more or less continuous weevil Anthonomus grandis is rotated with plies; in the second “type” lamellae are formed respect to the overlying layer by an angle of by parallel macrofibres. about 72o (LÉOPOLD et al. 1992). Fibre We think that there is some evidence that both patterning is discussed as being controlled by may be the endpoints of a ply-balken the epidermal cells and/or induced continuum”. Contrary to DENNELL (1976), mechanically or is disposed by self assembly we found in Geotrupes stercocorus (now (e.g., RICHARDS 1951; HEPBURN 1972; ZELAZNY Anoplotrupes stercorosus) plies instead of & NEVILLE 1972; 1975; DENNELL 1978; “balken”. Further, occasionally the innermost LÉOPOLD et al. 1992). The possible mechanical “lamellae” of endocuticles are not broken differences between “balken” versus “plies”, down in “balken”, but form a more or less however, has, to our knowledge, not been continuous ply as shown in Anthaxia fulgurans considered as yet. and Otiorhynchus ovatus. Moreover, adjacent “balkens” may anastomose and may be Acknowledgement organized in networks of macrofibrils (see citations above) and often the differentiation We thank Dr. A. RIEDEL, State Museum of between “balken” and plies seems rather Natural History in Karlsruhe, for the beetle subjective as a “balken” can reach a specimens, and Prof. Dr. V.B. MEYER- considerable width (not shown). However, ROCHOW, Bremen, for linguistic advice. as studied by TEM and SEM the macrofibres of the “balken cuticle” in the weevil Antho- Literature nomus grandis develop as discrete units and not as plies. Macrofibres are secreted after BARBAKADZE, N., ENDERS, S., GORB, S., & ARZT, E. eclosion as a lattice-like endocuticle in the form (2006): Local mechanical properties of the head articulation in the beetle Pachnoda of layers of parallel rod- or beam-shaped marginata (Coleoptera, ). Journal branching macrofibres, which are joined to of Experimental Biology 209: 722-730. adjacent macrofibres above and below. The BIEDERMANN, W. (1903): Geformte Sekrete. spaces between the macrofibres are assumed Zeitschrift für allgemeine Physiologie 2: to be filled with a probably proteinaceous 395-480. On the architecture of beetle elytra 203

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ZELAZNY, B., & NEVILLE, A.C. (1972) Quantitative *zzt. Staatliches Museum für Naturkunde studies on fibril orientation in beetle endo- Karlsruhe cuticle. Journal of Insect Physiology 18: 2095- Abteilung Biowissenschaften 2121. Referat Entomologie Erbprinzenstr. 13 Dipl.-Biol. Thomas van de Kamp* D-76133 Karlsruhe Prof. Dr. Hartmut Greven Institut für Zoomorphologie und Zellbiologie Heinrich-Heine-Universität Düsseldorf Universitätsstr. 1 D-40225 Düsseldorf E-Mail: [email protected] E-Mail: [email protected]